O-rings have been used to accomplish seals in various housings to prevent the passage of liquids or gases therethrough. Positioning the O-ring has been a problem especially in housings where the O-ring groove is to be seated is internal of the housing. The difficulty is to seat the O-ring in the proper position internally of any housing. Seating of O-rings to cylindrical parts to facilitate the proper sealing of these parts has been the object of several attempts in the past. U.S. Pat. Nos. 3,268,993 (Conner); 3,281,927 (Buslaff) and 4,821,398 (Hillstead) relate to the use of O-rings or similar rings in assemblies. In Conner a tool that applies locking rings externally to an assembly is described. Conner's locking ring illustrated in FIG. 13 of his patent is not elastic and his tool would be difficult to use for O-ring applications. Buslaff describes the use of a tool for expanding a tube or elastic assemblies for facilitating the subassembly with inelastic members of various devices. Buslaff's device is designed particularly for the dilation of the end portions of elastic tubes to permit their assembly with rigid annular or tubular parts that are to be tightly encircled by the end portions of the elastic tubes. Hillstead describes a tool that manufactures a sealed joint. Hillstead teaches that an O-ring is pushed onto an outer surface of a barrel member at the distal end of this barrel member. There is a need in the prior art for a simple device for the insertion of an O-ring internally of a tubular assembly.